1. Technical Field
The present invention relates to a rotary connector in which a stator housing and a rotor housing which are rotatably combined are electrically connected by a flexible cable, and particularly, to a rotary connector in which a rotor housing is constructed by an upper rotor and a lower rotor which are connected by snapping, etc.
2. Related Art
A rotary connector includes a stator housing fixed to an assembly of a combination switch, which is provided in a steering system of an automobile, or the like, a rotor housing attached to a steering wheel, a flexible cable housed within an annular housing space formed between these housings, and the like, and is used as an electrical connecting means, such as an air bag inflator, which is attached to a steering wheel with a limited number of revolutions.
In the related art, in such rotary connectors, a rotary connector in which an upper rotor and a lower rotor constitutes a rotor housing, and the lower rotor and the upper rotor are combined and integrated in the final stage of an assembling process, thereby enabling the stator housing to be mounted on the rotator housing is known (for example, refer to U.S. Pat. No. 6,435,886 which corresponds to Japanese Unexamined Patent Application Publication No. 2002-58150 (pages 4-6, FIG. 2)). FIG. 8 is a sectional view for explaining a schematic construction of this related-art rotary connector. The rotary connector shown in this drawing generally includes a stator housing 20, a rotor housing 21 rotatably mounted on the stator housing 20, a movable body 23 rotatably arranged within an annular housing space 22 formed between the housings 20 and 21, and a beltlike flat cable (flexible cable) 24 housed within the housing space 22 so as to be able to be wound and rewound.
The stator housing 20 is constructed by integrating an outer tubular body 25 and a bottom cover (bottom plate) 26, which are made of a synthetic resin, by snapping, etc. A holding wall 25a is formed at an upper end of the outer tubular body 25 so as to protrude inward, and a circular center hole 26a is formed in the middle of the bottom cover 26. Further, the rotor housing 21 is constructed by integrating an upper rotor 27 and a lower rotor 28 made of synthetic resin by snapping, etc., and in the upper rotor 27, a ring-shaped top plate 27a and an inner tubular body 27b which extends downward from the inner peripheral edge of the top plate are integrally formed. In the lower rotor 28, a substantially cylindrical wall portion 28a and a flange 28b which protrudes outward from a lower end of the wall portion are integrally formed, and the upper rotor 27 and the lower rotor 28 are integrated by fixing the cylindrical wall portion 28a to an inner wall portion of the inner tubular body 27b by snapping, etc. In addition, when the upper rotor 27 and the lower rotor 28 are integrated in this way, it is desirable that an outer peripheral edge of the top plate 27a of the upper rotor 27 is made to slidably face the upper face of the holding wall 25a of the outer tubular body 25, and the flange 28b of the lower rotor 28 is made to face the lower face of the inner peripheral edge of the bottom cover 26. By such a construction, the stator housing 20 is rotatably mounted on the rotor housing 21 in a state where axial rattling is suppressed. Further, since the outer peripheral surface of the flange 28b is made to face the bottom cover 26 with a required clearance, radial rattling the rotor housing 21 with respect to the stator housing 20 is suppressed.
The movable body 23 and the flat cable 24 are housed within the housing space 22. The movable body 23 is constituted by a plurality of rollers 23a and a ring-shaped rotary plate (roller holder) 23b, and the rotary plate 23b molded from synthetic resin is rotatably placed on an upper face of the bottom cover 26. Each roller 23a is rotatably supported on the upper face of the rotary plate 23b. Further, the flat cable 24 is reversed in winding direction on the way by a specific roller 23a in the housing space 22. In addition, although not shown, both longitudinal ends of the flat cable 24 are connected with lead blocks, and the lead blocks are respectively fixed to given positions of the stator housing 20 and the rotor housing 21. By electrically connecting an external connector or an external lead to these lead blocks, the flat cable 24 is electrically connected with an external circuit.
In the rotary connector constructed in this way, when the rotor housing 21 (the upper rotor 27 and the lower rotor 28) is rotated in any of forward and reverse directions with respect to the stator housing 20 (the outer tubular body 25 and the bottom cover 26), a reversed portion of the flat cable 24 moves in the same direction by a rotational amount smaller than the upper rotor 27, and along with this, the movable body 23 also moves in the same direction. As a result, the flat cable 24 of about twice the length of this travel distance is paid out from the inner tubular body 27b of the upper rotor 27, and is rewound toward the outer tubular body 25, or on the contrary, is paid out from the outer tubular body 25, and is wound toward the inner tubular body 27b. 
In the aforementioned related-art rotary connector, axial downward movement of the rotor housing 21 is suppressed by making the outer peripheral edge of the top plate 27a abut on the upper face of the holding wall 25a of the outer tubular body 25, and axial upward movement of the rotor housing 21 is suppressed by making the lower face of the flange 28b of the lower rotor 28 face the upper face of the inner peripheral edge of the center hole 26a of the bottom cover 26. Further, radial movement of the rotor housing 21 is suppressed within a predetermined range by making the outer peripheral edge of the top plate 27a face the holding wall 25a of the outer tubular body 25 radially, and making the outer peripheral edge of the flange 28b of the lower rotor 28 face the bottom cover 26 radially. However, since the outer peripheral edge of the top plate 27a is largely separated from the rotation center of rotor housing 21, under the influence of thermal expansion or the like during resin molding or at high temperature, the outer peripheral edge of the top plate 27a tends to cause deformation such as warpage, or positional deviation during rotation, and the rotational speed of the outer peripheral edge of the top plate 27a is comparatively larger than other portions. Therefore, during the rotation of the rotor housing 21, the outer peripheral edge of the top plate 27a stops sliding smoothly with respect to the holding wall 25a of the outer tubular body 25. As a result, there is a problem in that abnormal noises are generated from a sliding portion.